Show me how to merge and unmerge cells in Microsoft Excel 2007

Excel -> Microsoft Excel 2007

Problem: Certain cells, especially column headers, need to span multiple rows or columns.

Open Microsoft Excel 2007
Select two or more contiguous cells
On the "Home" tab, on the "Alignment" section, click the drop-down menu next to the "Merge & Center" button (the small down arrow next to the button that has a lowercase "a" with arrows pointing to the left and right)
Click the "Merge & Center" item or the "Merge Cells" item
Select the new, merged cell
On the "Home" tab, on the "Alignment" section, click the drop-down menu next to the "Merge & Center" button (the small down arrow next to the button that has a lowercase "a" with arrows pointing to the left and right)
Click the "Unmerge Cells" item